1. Technical Field
The present invention relates to a hole machining tool which is inserted into a pilot hole formed in advance in a workpiece to cut the inner surface of the pilot hole.
2. Background Art
As such a type of hole machining tool, a reamer in which an edge portion having a cutting edge is soldered to a front end of a tool body rotating about an axis line and having a longitudinal cylinder shape is known. The reamer rotates about the axis line, is fed in the axial direction, is inserted into a pilot hole formed in advance in a workpiece to cut the inner surface of the pilot hole with the cutting edge formed in the edge portion, thereby forming a machined hole having a predetermined inner diameter.
In such a hole machining tool in which the edge portion is soldered to the tool body, the position of the cutting edge in the diameter direction cannot be adjusted and thus the position of the cutting edge is determined by means of soldering precision. Accordingly, it is not possible to cope with the machining of a hole having a very small dimensional tolerance.
Therefore, for example, as described in JP-A-2002-160124, there is suggested an insert type reamer in which an insert having a cutting edge is detachably attached to the front end of the tool body and a positioning mechanism for adjusting a position of the cutting edge of the insert in the diameter direction of the tool body is provided. FIGS. 7 and 8 show an example of the known insert type reamer having the positioning mechanism.
The reamer 1 shown in FIGS. 7 and 8 has a tool body 2 rotating about an axis line O and having a longitudinal cylinder shape. A recessed portion 3 opened to the front side of the tool body 2 and the outside in the diameter direction of the tool body 2 is formed in a front outer periphery of the tool body 2 and an attachment seat 4 is formed on the rear side of the recessed portion 3 in the tool rotation direction T. As shown in FIG. 8, a plurality of guide pads 5 is disposed on the outer periphery of the tool body 2 with a constant gap in the circumferential direction. The guide pads interfering with the recessed portion 3 and the attachment seat 4 extend from the recessed portion 3 and the attachment seat 4 to the rear end of the tool body 2 and the other guide pads 5 extend to the front end of the tool body 2.
A panel-shaped insert 6 having a cutting edge 6A is attached to the attachment seat 4 in a state where the thickness direction thereof is matched with the tool rotation direction T, and is fixed thereto with a clamp screw 7.
The cutting edge 6A of the insert 6 is directed to the outside in the diameter direction of the tool body 2 and the front end side of the tool body 2 and two adjustment screws 8 and 9 as an adjustment mechanism for adjusting the position of the insert in the diameter direction are disposed in the inside of the insert 6 in the diameter direction of the tool body 2 so as to be arranged in the axial direction O. The adjustment screw located on the rear end side of the tool body 2 is a first adjustment screw 8 and the adjustment screw located on the front end side of the tool body 2 is a second adjustment screw 9. The front end surfaces of the first and second adjustment screws 8 and 9 abut a surface of the insert 6 facing the inside in the diameter direction of the tool body 2. A receiving hole 10 opened to the outside in the diameter direction of the tool body 2 is formed on the side of the attachment seat 4 close to the rear end of the tool body 2 and an adjustment wedge 11 for adjusting the position of the insert 6 in the axial direction O is inserted into the receiving hole 10.
The reamer 1 having the above-mentioned configuration is fitted to a primary shaft end of a machining tool, is fed to the front end side in the axial direction O with the rotation about the axis line O, is inserted into a pilot hole formed in advance in a workpiece to cut the inner surface of the pilot hole with the cutting edge 6A of the insert 6, thereby forming a machined hole having a predetermined inner diameter.
At the time of performing the cutting, the guide pads 5 slide on the inner surface of the machined hole and thus the fluctuation of the axis line O of the reamer 1, thereby enhancing the dimensional precision.
In the reamer 1 having the above-mentioned configuration, the inclination angle (back taper) of the cutting edge 6A formed in the insert 6 about the axis line O and the position of the cutting edge 6A in the diameter direction of the tool body 2 can be adjusted using the first adjustment screw 8 and the second adjustment screw 9, thereby forming the machined hole having a predetermined inner diameter with excellent dimensional precision. In addition, it is possible to cope with a very small dimensional tolerance of a machined hole. By appropriately attaching the back taper, it is possible to prevent unnecessary contact between the inner surface of the machined hole and the insert 6, thereby reducing cutting resistance.
However, in the reamer 1, since the panel-shaped insert 6 is attached in a state where the thickness direction thereof is matched with the tool rotation direction, it is necessary to open large the recessed portion 3 located on the front side of the attachment seat 4 in the tool rotation direction T. For example, in the reamer 1 shown in FIG. 5, the recessed amount of the portion recessed to the inside in the diameter direction of the tool body 2 from a section of the recessed portion 3 perpendicular to the axis line O is about ⅖ of the outer diameter of the tool body 2 (⅘ of the radius of the tool body 2) and the circumferential size of the recessed portion 3 is in the range of ⅕ to ¼ of the circumference of the tool body 2. Since the recessed portion 3 occupies a large portion of the tool body 2, the weight balance is poor in the section perpendicular to the axis line O and the movement at the time of rotating the tool body 2 about the axis line O at a high speed is not balanced. Accordingly, the position of the axis line O is disturbed, thereby not forming a machined hole having a high circularity with excellent dimensional precision.
In order to form the recessed portion 3 and the attachment seat 4 large, a plurality of guide pads 5 extend to the rear end of the tool body 2 from the recessed portion 3 and the guide pads 5 does not slide on the machined hole with good balance on the front end side of the tool body 2, thereby disturbing the axis line O of the reamer 1. When the recessed portion 3 is large along the axis line O, the guide pads 5 are shortened, thereby increasing the disturbance of the axis line O.
It is necessary to form the recessed portion 3, the clamp screw hole 12 into which a clamp screw 7 is screwed, adjustment screw holes 13 and 13 for receiving two adjustment screws 8 and 9, and the receiving hole 10 for receiving the adjustment wedge 11 in the front end portion of the tool body 2 and portions of the tool body 2 to be cut out increase, thereby reducing the rigidity of the tool body 2. Accordingly, a vibration may occur at the time of rotating the tool body 2 at a high speed. Specifically, when the reamer 1 has a small diameter, the recessed portion 3, the clamp screw hole 12, there is no space for forming the adjustment screw holes 13, and the receiving hole 10, thereby not providing the insert type reamer having the above-mentioned adjustment mechanism.
The adjustment mechanism for adjusting the back taper and the adjustment mechanism for adjusting the position in the diameter direction of the tool body 2 are embodied by the first and second adjustment screws 8 and 9. Accordingly, for example, when the back taper is first adjusted and then the position in the diameter direction of the tool body 2, the previously adjusted back taper varies and the back taper should be adjusted again. Therefore, much time and labor is required for adjusting the insert 6 and the positioning of the insert 6 could not be performed simply and precisely.